MEMS devices include micro-structures that move in an operation such as sound or motion sensing. The micro-structures may be formed by selective etch of a silicon, polysilicon or other material that is formed as part of, or later bonded to, a substrate. Membranes, flexible or cantilever beams, inertial masses for gyroscopes, accelerometers, micro-mirrors and other movable micro-structures may be formed for different applications. The micro-structures may be formed with a support in the form of a sacrificial material such as, for example, a nitride or oxide to protect and support the micro-structures during processing. After the micro-structure is complete, the micro-structure must be “released” by removing this sacrificial material. Removal of a sacrificial material is sometimes performed using an etchant in solution. The use of dilute etchant results in water (deionized water) being left in the spaces around and beneath the micro-structure. Application of a solvent may then be used to attempt to remove the water. A spinning step and a hot bake step may be used to remove the residual water that remains after the solvent is applied. However, water molecules sometimes remain on the device even after these process steps, and the residues cause stiction (that is, the MEMS structures do not move freely), structure crash (MEMS micro-structure may collapse on the underlying substrate), and these processes may cause the micro-structure to change shape or be warped, resulting in poor performance and reduced device yield.
As MEMS structures become increasingly important, for example to form MEMS microphones or other sensors for portable consumer devices, the need for efficient and reliable production of these devices continues to increase.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not drawn to scale.